Valve bags have been used for many years for packaging a wide variety of materials including cement and fertilizer. Valve bags are those having a small opening, smaller than open top bags wherein the entire top of the bag is open. Valve bags have an important advantage of easy filling through a valve structure, yet the valve may be self-closing after filling, due to the weight and volume of the filled contents. Also, valve bags are often used where the contents of the bag may be dusty and may prevent satisfactory and positive sealing of the bag. A number of prior designs for valve bags have been ones wherein the valve was a separate structure, often of a thin material, in order to provide the necessary antisift qualities to the valve after filling the bag. This was shown in U.S. Pat. Nos. 2,895,387; 3,394,871; and 3,221,789, and considerable cost and complexity were involved in the manufacture of the bags in order to insert this separate valve sleeve, position it properly, and fix it in position.
Practically all valve bags were produced as individual bags, the valve being manually inserted onto a filling spout, and the bag filled with the desired contents and then removed from the spout. Often the valve was tucked inside the bag by the operator so that the valve would be closed by the weight and bulk of the contents when the bag was laid flat. This required considerable labor cost in the filling of the bag because such manual handling for filling was slow, tedious, and often dangerous if the bags were being filled with toxic or hazardous material.
U.S. Pat. No. 3,746,246 showed a valve bag not requiring any separate supplemental valve sleeve to be inserted during its manufacture, the valve being constructed from the overlapping material of the bag itself. However, the bags still were separate, individual bags which required the manual operator to deftly manipulate the valve of the bag onto the filling spout during the filling operation and manually remove the bag from the spout upon completion of the filling, and hence this was also a slow filling operation, involving considerable labor expense. A similar construction was found in U.S. Pat. No. 3,833,166.
U.S. Pat. Nos. 3,559,874; 3,583,127; 3,699,746; 3,791,573; and 3,817,017 disclosed an interconnected chain of bags with a tunnel at the top edge for guidance of this chain of bags onto a mandrel of a bag-filling machine, with the bags being open-top bags for filling.